In general roller ball pens have a pen body in which a replaceable roller ball cartridge is held in place such that a user may write with the pen. The roller ball cartridge has a writing tip and a butt end. Usually the pen body has two pieces detachably held together by threads, for example. In order to replace the roller ball cartridge the two pieces are separated and the spent roller ball cartridge is removed and a replacement roller ball cartridge is inserted into one of the two pieces and the other piece is attached back into place. In some cases a spring or other biasing element abuts the butt end of the roller ball cartridge and the it inside of the body, such that the spring biases the writing tip out of the pen body. The spring or biasing element also provides a certain feel to the user, because, depending on the biasing force, the roller ball cartridge will have a certain recoil within the body while the user is writing with the pen. The prior art pens can only provide one tension, which is set by design, and a user must be satisfied with the feel of the particular pen chosen. Therefore, there is a need in the art for a roller ball pen for which the user can set the biasing force to meet the user's particular needs.